6107 BERKSHIRE DR 2018-01-02 MF Import

ADaPT Engineering, Inc. Western Wireless Corporation ADaPTJob No, WA98-992 April I, 1998 Page 8 a Table 4 Constant of Horizontal Subgrade Reaction (nh) Depth (feet) nh (pci) 0-2 0 2-7 50 7-20 70 20-29 50 _= Construction Considerations: At this site, the near surface silty gravelly sand weathered till soils are medium dense to dense in consistency. The underlying native glacial till soils is dense to very dense as well. Ilolvever, a perched groundwater condition was encountered at a depth of 21 feet below the ground surface. In our opinion, caving and sloughing of the drilled pier shaft sidewalls may be expected and at least some raveling of the drilled pier shaft sidewalls can be expected. Therefore, the foundation drilling contractor should be prepared to case the excavation to prevent raveling, caving and/or sloughing of the pier shaft sidewalls if caving conditions are encountered during drilling. Depending on the season of construction and the depth of pier penetration, dewatcring of the drilled shaft may or may not be required. Alternatively, the use of bentonite slurry could be utilized to stabilize the drilled pier excavation. The drilling contractor should be prepared to clean out the bottom of the pier excavation if loose soil is observed or suspected, with or without the presence of slum,or ground�..,rer. As a minimum, we recommend that the drilling contractor have a cleanout bucket on site to retrieve loose soils and/or mud from the bottom of the pier. If groundwater is present within the pier hole, we recommend that the foundation concrete be tremied from the bottom of the hole to displace the water and minimize the risk of contaminating the concrete mix. The Drilled Shaft Manual published by the Federal Highway Administration recommends that concrete be placed by tremie methods if more than 3 inches of water has accunndated in the excavation. Structural Fill The following comments, recommendations, and conclusions regarding structural fill are provided for design and construction purposes: Materials: Structural fill includes ^ny fill materials placed under footings, pavements, driveways, and other such structures. 1)pical materials used for structural fill include: clean, well -graded sand and gravel (pit -run); clean sand; crushed rock; controlled -density fill (CDF); lean -mix concrete; and various